Exhaust-gas-turbocharged internal combustion engines are nowadays often fitted with air-gap-insulated exhaust manifolds which are expediently produced in a two-shell design from thin-walled sheet-metal parts. The turbine housing is generally composed of cast materials with correspondingly greater wall thicknesses.
With air-gap-insulated manifold technology, the heat loss from the hot exhaust gas and likewise the surface temperature are reduced in relation to conventional cast manifolds on account of the lower masses. A greater amount of thermal energy is therefore made available to the downstream turbine of the exhaust-gas turbocharger for power conversion.
Air-gap-insulated manifolds are used in combination with both single-channel and also twin-channel turbine housings. Twin-channel turbine housings are used with so-called pulse supercharging, in which, for example in the case of a 4-cylinder or 6-cylinder engine, the exhaust-gas flows of in each case 2 or 3 cylinders are combined in groups and supplied in separate pipe lines to in each case one channel in the turbine housing. The individual channels in the turbine housing are separated from one another from the turbine housing inlet to the outlet from the spiral by a partition. In twin-channel turbine housings, the dynamic energy (pulsation) of the exhaust gases is additionally utilized for power conversion by means of the separation of individual exhaust gas flows.
With such complex components, however, the connecting technology between the thin-walled air-gap-insulated manifold and the comparatively thick-walled cast turbine housing has often proven to be relatively critical. On account of the available installation space, of the heat losses and leakage losses and on account of assembly requirements, the connection between the air-gap-insulated manifold and the cast turbine housing is often formed as a welded connection. With this type of connection in particular, problems arise on account of the materials, which are different for production reasons, of the air-gap-insulated manifold and of the cast turbine housing.
A further disadvantage, at least in the case of the twin-channel design of the turbine housing, is that the gas flows of the separate channels influence one another on account of leaks at the sliding connections within the air-gap-insulated manifold and in the region of the partition at the inlet into the turbine housing. The pulsation effect is therefore reduced as a result of the so-called “crosstalk” of the gas flows.